In recent years advances in theory and in research techniques have led to a better understanding of the manner in which the mammalian immune response system operates. It is now accepted that when antigens are introduced into the mammalian body, lymphocyte cells synthesise antibody molecules which have the property of binding to specific sites (determinants) on the antigens and rendering them innocuous. The deliberate stimulation of the immune response system is a common technique for the production of antisera, the applications of which are legion (e.g. in the production of vaccines, in pathology and in medical and zoological research).
One problem inherent in antisera produced in this way is the variation in physiological activity that they exhibit.
This effect may be attributed, at least partially, to the number of specific antibodies produced as a result of the stimulating immunization. In addition to the antibodies produced to antigenic impurities in the immunizing medium, each antigen to which an antibody is required may possess a plurity of determinant sites. Thus, the "cocktail" of antibodies produced by the body will be complex, its composition may be variable, synergistic effects may be evident and when administered to a different mammal, even within the same species its physiological effect is likely to be different as a result of differences in the combination of determinants present in the donor mammal and in the recipient.
A further problem in the production of antisera in this way is the cost of extraction and purification which renders samples of clinical purity expensive.
Research in the field of molecular biology has now provided an alternative source if antibodies. It has been discovered that fusion between lympocyte cells and myeloma cells derived from mammals (e.g. mice and rats) can produce hybrid cells capable of replication in vitro, (see Kohler and Milstein, Nature 256, 495-597). Such hybrid cells have the property of secreting an antibody of predefined specificity. This specifity is that of the antibody produced by the lympocyte involved in the fusion. The hybrid cells may be cloned and grown in stable culture to produce in the culture supernatant samples of antibody to a specific determinant. Antibodies produced in this way are known as monoclonal antibodies in the art.
The general method of production of hybrid cell lines of the type described above comprises the steps of immunizing a animal (usually a rat or mouse, but not necessarily one of these) with an antigen to which a monoclonal antibody is required. After allowing time for the immune system to generate lymphocytes secreting the antibodies to the antigen, the animal is sacrificed and a suspension of spleen cells is prepared. Fusion between these cells and myeloma cells is achieved by bringing them into contact in the presence of a fusion promoter (e.g. polyethyleneglycol). A small percentage of the cells fuse to produce hybrid myeloma cells. The immunization results in a plurality of different lymphocytes each secreting antibody to a different antigenic determinant, and these characteristics are transferred genetically to the hybrid cells. It is possible, by careful screening, to isolate from a culture of hybrid cells, a cell having the desired specificity. Such cells may be cloned and cultured.
The advantage at this technique is that it provides a source of a specific antibody uncontaminated by antibodies raised to other determinants either on the antigen with which the mammal was immunized or on antigenic impurities in the immunizing material. Another advantage of the technique is that antigen not available in a pure form for screening assays and present in the immunizing material at low concentrations, may be used.
Clearly the success of the process relies upon an efficient screening assay to be applied after the cell fusion stage.
The present invention concerns a monoclonal antibody to leukocyte interferon (also known in the art as interferon-.alpha.). This protein, or group of proteins (present evidence suggests about 15 distinct molecular entities) is currently the centre of considerable interest in the medical world following the discovery of its antitumour and antiviral activity. Interest amongst researchers worldwide has created a demand for substantial quantities of interferon to be used not only for clinical trials but also by research establishments attempting to produce a more detailed picture of the mammalian immune response system and the action of interferons therein. Considerable progress has been made in the characterisation of human (and mouse) interferons including amino acid compositions and aminoterminal sequences.
The size and nature of this demand necessitates large scale production including extensive purification stages, the complexity of which renders interferon prohibitively expensive for routine use.
Interferon is available from lymphoblastoid cells, from white blood cells (buffy coat lymphocytes), and from genetically modified bacteria. Improvements in purification techniques have recently allowed the purification of interferons to homogeneity. Two of the three species of interferon have been purified to this point, namely: fibroblast interferon (interferon .beta.) and leukocyte interferon.
The monoclonal antibody the subject of the present invention may be used in purification process which results in a purity of interferon hitherto not available in substantial quantities.